Electrode with reversibly sealed fluoride sensing crystal

Abstract

A free fluoride ion sensitive electrode with longer service life can be obtained by eliminating the use of any cement or similar adhesive to hold the fluoride sensing crystal of the electrode in place within the rest of the structure of the electrode, using instead a pressure sealed combination of the fluoride sensing crystal and upper and lower elastomeric gaskets. This arrangement also permits replacing the crystal and sealing gaskets if needed, without replacing any of the other components of the electrode.

What is claimed is:  
     
       1. A free-fluoride-ion-sensitive electrode comprising: 
       (A) a substantially liquid-impermeable solid fluoride-sensing crystal that is constituted of one or more fluoride-ion-sensitive solid, crystalline, substantially water-insoluble fluorides;  
       (B) first and second solid elastomeric gaskets that form a sealing array with the fluoride-sensing crystal;  
       (C) a primary container body constituted of electrically insulating material and having walls surrounding a central cavity that extends completely through the primary container body, thereby forming a first and second end of said central cavity, said central cavity having a size and a shape such that a sealing array among the primary container body, the fluoride-sensing crystal, and said first and second elastomeric gaskets is formed;  
       (D) means for maintaining the sealing array among the fluoride-sensing crystal, the first and second elastomeric gaskets, and the primary container body when they are jointly rotated, said means not including use of any cement or adhesive or any incorporation of the fluoride-sensing crystal into a cohesive unitary solid from which it can not be removed intact without dividing all parts of the unitary solid that do not consist of the fluoride-sensing crystal into at least two separate pieces;  
       (E) means for dividing the central cavity of the primary container body so as to constitute jointly with the primary container body, the fluoride-sensing crystal and at least one of the first and second elastomeric gaskets, boundaries of a liquid- and vapor-tight portion of the central cavity of the primary container body;  
       (F) a volume of a first liquid ionic solution of known composition and concentration confined within said substantially liquid- and vapor-tight portion of the central cavity of the primary container body and in physical contact with the fluoride-sensing crystal;  
       (G) a first reference electrode enclosed within said substantially liquid- and vapor-tight portion of the central cavity of the primary container body, said first reference electrode including a metallic electrical conductor that is in physical contact with the first liquid ionic solution but is not in physical contact with the fluoride-sensing crystal; and  
       (H) an electrically conducted lead component that is in physical contact with both the metallic electrical conductor part of the first reference electrode and a point outside said substantially liquid- and vapor-tight portion of the central cavity of the primary container body but is not in physical contact with the fluoride-sensing crystal or with the first ionic solution,  
       wherein: the central cavity of the primary container body has a central portion that is cylindrical; a first end portion of the central cavity of the primary container body has a shape of a cylinder that is concentric with but has a larger diameter than the cylindrical central portion of the central cavity, so that the primary container body in said first end portion has a bounding wall surface that consists of two concentric cylinders joined by an annular disk with a circular center hole, the disk and center hole both being concentric with said concentric cylinders; and a solid portion of said annular disc and an end portion of the walls of the primary container body surrounding the central cavity bound a space in which the sealing array of said fluoride-sensing crystal and said first and second elastomeric gaskets is retained. 
     
     
       2. A free-fluoride-ion-sensitive electrode according to  claim 1 , wherein the fluoride sensing crystal is a solid cylinder and each of the first and second elastomeric gaskets is a cylinder with a cylindrical hole therethrough or is a torus. 
     
     
       3. A free-fluoride-ion-sensitive electrode according to  claim 2 , wherein: the means for maintaining the sealing array of the fluoride-sensing crystal, the first and second elastomeric gaskets, and the primary container body comprises the following components: 
       (A′) male screw threads on an exterior first end portion of the walls of the primary container body; and  
       (B′) a first end cap component comprising:  
       (1) a primary cylinder portion having a concentric cylindrical hole therethrough, so that the primary cylinder portion has exterior and interior walls and distinct first and second ends of each of the exterior and interior walls;  
       (2) a retainer portion joined to the primary cylinder portion at its second end; and  
       (3) a continuous zone of female screw threads on at least a part of the interior wall of the primary cylinder portion, said female screw threads being matable with the male screw threads on the exterior first end portion of the walls of the primary container body when these male screw threads are inserted into the first end of the interior walls of the first end cap component,  
       said retainer portion and said primary cylinder portion together forming a liquid-tight container to retain the sealing array of said fluoride-sensing crystal and said first and second elastomeric gaskets, (i) said male screw threads on the primary container body, (ii) said first end cap component, (iii) said primary cylinder portion of the first end cap component, (iv) said concentric cylindrical hole therethrough, (v) said exterior and interior walls of the first end cap component, (vi) said female screw threads on at least a zone of said interior walls, (vii) said retainer portion of the first end cap component, and (viii) a hole therethrough all forming a torque-limited-screwed, temperature-stable sealing container around the sealing array of the fluoride-sensing crystal and the first and second elastomeric gaskets. 
     
     
       4. A free-fluoride-ion-sensitive electrode according to  claim 3 , wherein the means for dividing the central cavity of the primary container body is a plug of solidified potting resin through which electrically conducting lead component (H) passes. 
     
     
       5. A free-fluoride-ion-sensitive electrode according to  claim 4 , wherein: the central cavity through the primary container body has an enlarged zone which has two ends, both ends of said enlarged zone of the central cavity being within, rather than at either end of, the central cavity and both of the ends of the enlarged zone being between an end of the primary container body and the liquid- and vapor-tight portion of the central cavity that contains the first ionic solution of known composition, said enlarged zone being larger in cross-section than is another portion of said central cavity that is situated between the enlarged zone and one of said ends of said central cavity; and at least a portion of said plug of potting resin fits within said enlarged zone of the central cavity of the primary container body and has a larger cross-section than does a portion of said central cavity that is situated between the enlarged zone and said one of said ends of said central cavity. 
     
     
       6. A free-fluoride-ion-sensitive electrode according to  claim 5 , wherein a second end of the primary container body has a zone of male screw threads on its exterior surface and the second end of the central cavity through the primary container body is closed by a second end cap component comprising: 
       (1) a primary cylinder portion having a concentric cylindrical hole therethrough, so that the primary cylinder portion has exterior and interior walls and distinct first and second ends of each of the exterior and interior walls;  
       (2) a closure portion joined to the primary cylinder portion at the second end of its exterior and interior walls, said closure portion being a solid circular disk, except that electrical lead component (H) passes through it; and  
       (3) a continuous zone of female screw threads on at least a part of the interior wall of the primary cylinder portion, said female screw threads being matable with the male screw threads on the exterior second end of the walls of the primary container body when these male screw threads are inserted into the first end of the interior walls of the second end cap component.  
     
     
       7. A free-fluoride-ion-sensitive electrode according to  claim 6 , wherein the primary container body and the end caps are constituted of polytetrafluoroethylene and the first and second elastomeric gaskets are constructed of a copolymer of tetrafluoroethylene and perfluoro(methylvinylether). 
     
     
       8. A free-fluoride-ion-sensitive electrode according to  claim 3 , wherein the primary container body and any end cap or caps present in the free-fluoride-ion-sensitive electrode have a modulus of elasticity in flexure from 1.0×10 7  to 5.0×10 7  kg/m 2  and the first and second elastomeric gaskets are constructed of a fluorocarbon elastomer. 
     
     
       9. A free-fluoride-ion-sensitive electrode according to  claim 4 , wherein the primary container body and any end cap or caps present in the free-fluoride-ion-sensitive electrode are constituted of polytetrafluoroethylene and the first and second elastomeric gaskets are constructed of a copolymer of tetrafluoroethylene and perfluoro(methylvinylether). 
     
     
       10. A free-fluoride-ion-sensitive electrode according to  claim 5 , wherein the primary container body and any end cap or caps present in the free-fluoride-ion-sensitive electrode are constituted of polytetrafluoroethylene and the first and second elastomeric gaskets are constructed of a copolymer of tetrafluoroethylene and perfluoro(methylvinylether). 
     
     
       11. A free-fluoride-ion-sensitive electrode according to  claim 1 , wherein: the means for maintaining the sealing array of the fluoride-sensing crystal, the first and second elastomeric gaskets, and the primary container body comprises the following components: 
       (A′) male screw threads on an exterior first end portion of the walls of the primary container body; and  
       (B′) a first end cap component comprising:  
       (1) a primary cylinder portion having a concentric cylindrical hole therethrough, so that the primary cylinder portion has exterior and interior walls and distinct first and second ends of each of the exterior and interior walls;  
       (2) a retainer portion joined to the primary cylinder portion at its second end; and  
       (3) a continuous zone of female screw threads on at least a part of the interior wall of the primary cylinder portion, said female screw threads being matable with the male screw threads on the exterior first end portion of the walls of the primary container body when these male screw threads are inserted into the first end of the interior walls of the first end cap component,  
       said retainer portion and said primary cylinder portion together forming a liquid-tight container to retain the sealing array of said fluoride-sensing crystal and said first and second elastomeric gaskets, (i) said male screw threads on the primary container body, (ii) said first end cap component, (iii) said primary cylinder portion of the first end cap component, (iv) said concentric cylindrical hole therethrough, (v) said exterior and interior walls of the first end cap component, (vi) said female screw threads on at least a zone of said interior walls, (vii) said retainer portion of the first end cap component, and (viii) a hole therethrough all forming a torque-limited-screwed, temperature-stable sealed container around the sealing array of the fluoride-sensing crystal and the first and second elastomeric gaskets. 
     
     
       12. A free-fluoride-ion-sensitive electrode according to  claim 11 , wherein the means for dividing the central cavity of the primary container body is a plug of solidified potting resin through which electrically conducting lead component (H) passes. 
     
     
       13. A free-fluoride-ion-sensitive electrode according to  claim 12 , wherein: the central cavity through the primary container body has an enlarged zone which has two ends, both ends of said enlarged zone of the central cavity being within, rather than at either end of, the central cavity and both of the ends of the enlarged zone being between an end of the primary container body and the liquid- and vapor-tight portion of the central cavity that contains the first ionic solution of known composition, said enlarged zone being larger in cross-section than another portion of said central cavity that is situated between the enlarged zone and one of said ends of said central cavity; and at least a portion of said plug of potting resin fits within said enlarged zone of the central cavity of the primary container body and has a larger cross-section than does a portion of said central cavity that is situated between the enlarged zone and said one of said ends of said central cavity. 
     
     
       14. A free-fluoride-ion-sensitive electrode according to  claim 13 , wherein a second end of the primary container body has a zone of male screw threads on its exterior surface and the second end of the central cavity through the primary container body is closed by a second end cap component comprising: 
       (1) a primary cylinder portion having a concentric cylindrical hole therethrough, so that the primary cylinder portion has exterior and interior walls and distinct first and second ends of each of the exterior and interior walls;  
       (2) a closure portion joined to the primary cylinder portion at the second end of its exterior and interior walls, said closure portion being a solid circular disk, except that electrical lead component (H) passes through it; and  
       (3) a continuous zone of female screw threads on at least a part of the interior wall of the primary cylinder portion, said female screw threads being matable with the male screw threads on the exterior second end of the walls of the primary container body when these male screw threads are inserted into the first end of the interior walls of the second end cap component.  
     
     
       15. A free-fluoride-ion-sensitive electrode according to  claim 14 , wherein the primary container body and any end cap or caps present in the free-fluoride-ion-sensitive electrode are constituted of polytetrafluoroethylene and the first and second elastomeric gaskets are constructed of a copolymer of tetrafluoroethylene and perfluoro(methylvinylether). 
     
     
       16. A free-fluoride-ion-sensitive electrode according to  claim 11 , wherein the primary container body and any end cap or caps present in the free-fluoride-ion-sensitive electrode are constituted of polytetrafluoroethylene and the first and second elastomeric gaskets are constructed of a copolymer of tetrafluoroethylene and perfluoro(methylvinylether). 
     
     
       17. A free-fluoride-ion-sensitive electrode according to  claim 12 , wherein the primary container body and any end cap or caps present in the free-fluoride-ion-sensitive electrode are constituted of polytetrafluoroethylene and the first and second elastomeric gaskets are constructed of a copolymer of tetrafluoroethylene and perfluoro(methylvinylether). 
     
     
       18. A free-fluoride-ion-sensitive electrode according to  claim 13 , wherein the primary container body and any end cap or caps present in the free-fluoride-ion-sensitive electrode are constituted of polytetrafluoroethylene and the first and second elastomeric gaskets are constructed of a copolymer of tetrafluoroethylene and perfluoro(methylvinylether).